Development apparatus

ABSTRACT

A development apparatus for developing electrostatic images upon a moving image-bearing surface including flow baffle means for regulating the flow of developer to the development zone. The baffle means is positioned between a supply means and the development zone and extends inwardly of each of the ends of a development means which preferably comprises a magnetic brush. The baffle means comprises stationary magnetic brushes formed of developer material. The stationary magnetic brushes are adapted to limit the flow of developer at the end portions of the development means.

O United States Patent 11 1 1111 3,

Wilcox Oct. 28, 1975 [5 DEVELOPMENT APPARATUS 3,754,526 8/1973 Caudill118/637 [75] mentor: David G. Wilcox, West Webster 3,822,139 7/1974Westdale 118/637 Primary Examiner-Mervin Stein [73] Assignee: XeroxCorporation, Stamford, Assistant Examiner-Douglas Salser Conn. Attorney,Agent, or FirmPa1il Weinstein; Clarence [22] Filed: No 19, 1973 A.Green; James J. Ralabate [21] Appl. No.: 416,898 5 ABSTRACT Adevelopment apparatus for developing electrostatic [52] US. Cl. 118/637image u on a moving image-bearing surface includ- [51] [lilt- CLZ 603G15/08 ing flow baffle mqans for regulating the flow of le el. Fleld ofSearch 1 D oper to the development zone. The baffle means is po- 1sitioned between a supply means and the development zone and extendsinwardly of each of the ends of a de- [56] References Clted velopmentmeans which preferably comprises a mag- UNITED STATES PATENTS neticbrush. The baffle means comprises stationary 2,892,446 6/1959 Olden118/637 magnetic brushes formed of developer material- The 2,904,0009/1959 Fisher et a1. 118/637 Stationary magnetic brushes are adapted tolimit the 3,058,444 10/1962 Sugarman et a1. 1. 118/637 flow of developerat the end portions of the develop- 3,l33,834 5/1964 Sowiak 118/637 mentmeans. 3,648,656 3/1972 Ogawa 118/637 3,753,420 8 1973 Post et al.118/637 16 Claims, 10 -n8 Flgul'es US. Patent 0012511975 Sheet10f33,915,121

ll III-II US. Patent Oct.'28,1975

Sheet 2 of 3 FIG. 3

US. Patent Oct. 28, 1975 Hays/"g1 from housing along FIG. 70

Sheet 3 of 3 Developer How Rafe Distance from housi a/on roll 0x11; "9 9FIG. 8a

Haus/ngl FIG. Yew

DEVELOPMENT APPARATUS BACKGROUND OF THE INVENTION This invention relatesto a development apparatus for developing electrostatic images upon amoving imagebearing surface. Flow baffle means are included forregulating the flow of developer to the development zone. The flowbaffle means comprise stationary magnetic brushes.

In prior art magnetic brush development apparatuses, a problem hasoccurred with respect to the copy quality output of the electrostaticreproducing machines in which they are employed. In some machines a highbackground region is formed on each of the end portions of the copysheet due to higher flow rates of developer at the end portions of amagnetic brush development means. The higher flow rates at the ends ofthe magnetic brush development means are due at least in part to thepresence of fringe fields at the ends of the brush forming magnetswithin the development means which attract an increased amount ofdeveloper to the ends of the magnetic roll. The increased flow ofdeveloper coupled with fringe fields at the ends of the magnetic brushroll results in a higher density of developer at the ends of the rolland, therefore, a consequent increase in the background level on the endportions of the copy sheet.

In US. Pat. Nos. 3,648,656, granted March, 1972, and 3,754,526, grantedAugust, 1973, there are disclosed magnetic brush development apparatuseswherein magnetic field generating means are employed to prevent thedeveloper from being picked up by the end portions of the magnetic brushrolls. These patents use magnetic fields to control the flow ofdeveloper, but do not employ stationary magnetic brushes in accordancewith this invention to mechanically control the flow of developer.

The use of a magnetic means interposed between a bearing and a flow ofmagnetic particles is described in US. Pat. No. 2,996,162, grantedAugust, 1961, and in US. application Ser. No. 266,905, filed June 28,1972. In these devices a magnetic flux field produced by the magneticmeans entraps and aligns the magnetic granules into a brush which actsto seal the bearings from the flow of magnetic particles. The patent andapplication do not use the magnetic seal brushes as flow baffles toregulate the flow of developer to the development zone of a developmentapparatus.

SUMMARY OF THE INVENTION In accordance with this invention flow bafflemeans are provided for regulating the flow of developer to thedevelopment zone. The baffle means are positioned between the supplymeans and the development zone and extend inwardly of each of the endsof the development means and have a limited extension in the directionof movement of the development means. The baffle means, in accordancewith this invention, comprise stationary magnetic brushes which areeffective to limit the flow of developer at the end portions of thedevelopment means.

Preferably, in accordance with this invention, the development apparatuscomprises a magnetic brush development apparatus and the developmentmeans includes a magnetic brush support means, means for,

forming a magnetic brush of developer upon the support means, and meansfor moving the support means between the supply means and thedevelopment zone.

The stationary magnetic brush flow baffles of this invention arepreferably formed by means of a magnetic field generated externally ofthe development means. The magnetic field generating means preferablycomprises a permanent magnet and most preferably a magnet having a wedgeshape to provide a less abrupt flow rate disturbance. To provide afurther improvement in developer flow regulation at the ends of thedevelopment means, mechanical flow blocks separate from the stationarybrush flow baffles can be employed which are positioned between the flowbaffles and the supply means.

Accordingly, it is an object of this invention to provide a developmentapparatus including stationary magnetic brush flow baffle means toregulate the flow of developer to the development zone.

It is a further object of this invention to provide a developmentapparatus as above which comprises a magnetic brush developmentapparatus.

It is a still further object of this invention to provide a reproducingapparatus employing the above-noted development apparatus.

These and other objects of the invention will become more apparent tothose skilled in the art from the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a top view in partialcross-section of a prior art magnetic brush development means.

FIG. 2 shows a schematic view in partial cross-' section of anelectrostatographic reproducing machine in accordance with thisinvention.

FIG. 3 is a partial front view in partial cross-section along the line3-3 in FIG. 2.

FIG. 4 is a top view in partial cross-section of a magnetic brushdevelopment means in accordance with this invention.

FIG. 5 is a partial cross-section of a magnetic brush apparatus havingone embodiment of a flow baffle in accordance with this invention.

FIG. 6 is a partial cross-section of a magnetic brush apparatus having aflow baffle in accordance with a different embodiment of the presentinvention.

FIG. 7a and 7b comprise a graph and partial cross section respectivelyillustrating the flow regulating effect of a stationary brush formingmagnet in accordance with one embodiment of the invention.

FIGS. 8a and 8b comprise a graph and partial crosssection respectivelyillustrating the flow regulating effect of a stationary brush formingmagnet in accordance with apreferred embodiment of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1,there is shown a magnetic brush 1 formed in accordance with a prior artmagnetic brush roll design 2. The magnetic brush roll 2 comprises acylindrical shell 3 which has a stationary magnet 4 supported within it,which is adapted to orient and form a developer mix into a magneticbrush 1 for application to an electrostatic image on a movingimage-bearing surface. A generally normal field is provided along thelength of the magnet 4 except at the ends 5 and 6 where fringe fields 7and 8 are formed which have an additive effect with the normal field toprovide stronger magnetic fields at the ends of the magnet. This resultsin an increased amount of developer being picked up at the end portions9 and 10 of the mag brush roll 2 so that the resulting magnetic brush 1prior to contacting the image-bearing plate has a cross-sectionsubstantially as shown. The increased amount of developer material whichgoes into the portions 11 and 12 of the brush 1 at the ends of the roll2 results in a marked increase in developer flow at these portions and aconsequent reduction in developer life. Besides reducing developer lifethe increased flow rates at the end portions 9 and 10 of the roll 2coupled with the fringe fields 7 and 8, have a deleterious effect oncopy quality. When the brush 1 contacts the image-bearing surface, thebubous portions 11 and 12 of the brush are compacted such that they havean increased developer density. As a result, a greater portion ofbackground is developed by the end portions 11 and 12 of the magneticbrush 2 which when transferred to the final support sheet gives anundesirably high background appearance at each of the ends of the sheet.

In order to reduce the developer flow rates at the end portions 9 and 10of the magnetic brush roll 2 in accordance with this invention as shownin FIG. 2, baffle flow means are provided which comprise stationarymagnetic brushes 21 which are effective to regulate the flow ofdeveloper at the end portions 9 and 10 of the roll 2.

Referring now to FIG. 2 there is shown by way of example an automaticxerographic reproducing machine 30 which incorporates the magnetic brushflow baffles 20 and magnetic brush apparatus 31 of the presentinvention. The reproducing machine 30 depicted in FIG. 1 illustrates thevarious components utilized therein for producing copies from anoriginal. Although the magnetic brush flow baffles 20 and magnetic brushapparatus 31 of the present invention are particularly well adapted foruse in an automatic xerographic reproducing machine 30, it should becomeevident from the following description that they are equally well suitedfor use in a wide variety of processing systems including otherelectrostatographic systems and they are not necessarily limited intheir application to the particular embodiment or embodiments shownherein.

The reproducing machine 30 illustrated in FIG. 2 employs an imagerecording drum-like member 32, the outer periphery of which is coatedwith a suitable photoconductive material 33. One type of suitablephotoconductive material is disclosed in US. Pat. No. 2,970,906, issuedto Bixby in 1961. The drum 32 is suitably journaled for rotation withina machine frame (not shown) by means of shaft 34 and rotates in thedirection indicated by arrow 35 to bring the imagebearing surface 33thereon past a plurality of xerographic processing stations. Suitabledrive means M are provided to power and coordinate the motion of thevarious cooperating machine components whereby a faithful reproductionof the original input scene information is recorded upon a sheet offinal support material 36 such as paper or the like.

The practice of xerography is well known in the art and is the subjectof numerous patents and texts including Electrophotography by Schaffert,published in 1965, and Xerography and Related Processes by Dessauer andClark, published in 1965.

The various processing stations for producing a copy of an original areherein represented in FIG. 2 as blocks A to E. Initially, the drum 32moves the photoconductive surface 33 through a charging station A. Inthe charging station A, an electrostatic charge is placed uniformly overthe photoconductive surface 33 preparatory to imaging. The charging maybe provided by a corona generating device of the type described in U.S.Pat. No. 2,836,725, issued to Vyverberg in 1958.

Thereafter, the drum 32 is rotated to exposure station B wherein thecharged photoconductive surface 33 is exposed to a light image of theoriginal input scene information whereby the charge is selectivelydissipated in the light exposed regions to record the original inputscene in the form of a latent electrostatic image. A suitable exposuresystem may be of a type described in U.S. Pat. No. 3,062,l 10, issued toShepard son et al. in 1962. After exposure drum 32 rotates theelectrostatic latent image recorded on the photoconductive surface 33 todevelopment station C in accordance with the invention wherein aconventional developer mix is applied to the photoconductive surface 33of the drum 32 rendering the latent image visible. A suitabledevelopment station is disclosed in U.S. Pat. No. 3,707,947, issued toReichart in 1973. That patent describes a magnetic brush developmentsystem utilizing a magnetizable developer mix having ferromagneticcarrier granules and a toner colorant. The developer mix is broughtthrough a directional flux field to form a brush thereof, theelectrostatic latent image recorded on the photoconductive surface 33 isdeveloped by bringing the brush of developer mix into contact therewith.

Further details of the development apparatus which comprises developmentstation C will be described later by specific reference to the presentinvention.

The developed image on the photoconductive surface 33 is then broughtinto contact with the sheet 36 of final support material within atransfer station D and the toner image is transferred from thephotoconductive surface 33 to the contacting side of the final supportsheet 36. The final support material may be paper, plastic, etc., asdesired.

After the toner image has been transferred to the sheet of final supportmaterial 36 the sheet with the image thereon is advanced to a suitablefuser 37 which coalesces the transferred powder image thereto. One typeof suitable fuser is described in U.S. Pat. No. 2,701,765, issued toCodichini et al. in 1955. After the fusing process the sheet 36 isadvanced to a suitable output device.

Although a preponderance of the toner powder is transferred to the finalsupport material 36, invariably some residual toner remains on thephotoconductive surface 33 after the transfer of the toner powder imageto the final support material. The residual toner particles remaining onthe photoconductive surface 33 after the transfer operation are removedfrom the drum 32 as it moves through a cleaning station E. The tonerparticles may be mechanically cleaned from the photoconductive surface33 by any conventional means as, for example, the use of a blade as setforth in US. Pat. No. 3,740,789, issued to Ticknor in 1973.

It is believed that the foregoing description is sufficient for purposesof the present application to illustrate the general operation of anautomatic xerographic copier which can embody the magnetic brush flowbaffles 20 and magnetic brush apparatus 31 in accordance with thepresent invention.

Referring again to the development apparatus 31 it includes a storageportion or sump in a housing 41 for storing the developer material. Thetop of the housing may include an opening 0 that could have a removablecover or cap (not shown). The system could include a toner dispenser(not shown) disposed over the opening which periodically dispenses tonerinto the housing in a manner similar to that taught in US. Pat. No.3,608,792. Alternatively, the circulating system could be of the typewhere toner and/or toner plus carrier is added periodically by anoperator or an attendant to the machine.

The development apparatus 31 includes magnetic brush rolls 42 and 43.The magnetic brush applicator roll 42 includes a rotatably mountedsupport member in the form of a cylindrical shell or sleeve 44 and astationary permanent magnet 45 suspended within the sleeve. The magneticfield of the magnet is oriented to form a brush-like structure of thedeveloper mix. The applicator roll 42 is immersed in the sump 40 ofdeve1- oper material which comprises ferromagnetic carrier particles anda toner colorant. The developer mix is picked up by the outer supportsurface of the roll 42 by means of a pick-up magnetic field generated bystationary magnet 46 suspended within the sleeve 44, and is formed intoa brush-like structure for application to the photoconductive surface 33for development of the latent electrostatic image presented thereon.While only one applicator roll 42 is shown, any number of applicatorrolls could be employed as desired.

Continued rotation of the roll past the development zone brings themagnetic brush 47 into the field of a lifting magnetic brush roll 43.The lifting roll 43 attracts the developer mix from the magnetic brushapplicator roll 42 and carries it upward to be deposited on a slide 48from which it flows into a cross-mixer 49 for return to the sump 40. Thelifting roll 43 is also a magnetic brush roll and comprises acylindrical sleeve 50 'rotatably supported in the housing 41 and a fixedpermanent magnet 51 supported in a stationary position within thesleeve. It is also possible in accordance with this invention to employany desired number of lifting rolls 43. Further details of the apparatus31 of FIG. 1 can be gained from a consideration of the aforenoted U.S.Pat. No. 3,707,947. In accordance with this invention magnetic brushflow baffles 20 are provided to regulate the flow of developer at theend portions of the magnetic brush applicator roll 42.

Referring to FIGS. 2 and 3, the relative positions and generated bypermanent magnets 22 and 23. The stationary magnetic brushes 21 extendinwardly from the housing 41 and inwardly of the development means whichin the embodiment shown comprises the axial direction of the magneticbrush roll 42. The stationary magnetic brush baffles 20 are positionedbetween the supply means 52 and the development zone 53. They have alimited extension or width in the direction of movement of the mag brushroll 42. This is significant since it is apparent from the drawings thatthe baffles 20 do not act to seal the end portions 54 and 55 of the magbrush roll 42 from the developer mix. While they can reduce or eliminatethe flow of developer mix on the end portions 54 and 55 of the roll 42between the baffles 20 and the development zone 53, they are not sooperative between the baffles 20 and the supply means 52.

In order to form the stationary magnetic brushes 21 in accordance withthis invention, it is preferred to employ permanent magnets 22 and 23extending out from the sides of the housing 41 and positioned externallyof the housing. The magnets may be held in place by any desired meanssuch as, for example, the use of spring clips 56 as shown. The field ofeach magnet 22 and 23 is oriented as shown to form stationary magneticbrushes 21 extending outwardly from the bottom of the housing 41 towardthe applicator roll surface.

It is preferred in accordance with this invention that the stationarymagnetic brushes 21 extend out from the housing 41 toward the roll 42over less than the entire gap 57 between the housing and the roll. Thistype of a structure permits some developer flow at the end portions 54and 55 of the roll 42. The amount of developer flow which is permittedshould preferably be less than, or equal to, the rate of developer flowat the middle portion, in an axial sense, of the roll. This can resultas shown in FIG. 4, in a substantially uniform magnetic brush 47 beingformed over the entire operative length of the roll 42 or in one (notshown) with end portions of the brush having a reduced height ascompared to the axial middle portion of the brush. Comparing FIG. 4 toFIG. 1, the effect of the magnetic brush flow baffles 20 of thisinvention is clearly illustrated, namely, the bulbous portions 11 and 12of the brush 1 have been reduced to a height equal to or less than thatof the brush at the axial middle of the roll 42.

Referring again to FIG. 3, it is apparent that the magnetic brush 47 onthe surface of the roll is not formed over the entire axial length ofthe roll 42, but rather the length of the brush is dictated by thelength of the magnets 45 and 46 within the roll. Since the magneticbrush flow baffles 20 of this invention are directed at eliminating theeffect of the fringe fields at the ends of the magnet 45, it ispreferred that they extend inwardly past the ends 58 and 59 of themagnet 45 a desired amount to offset the effect of the fringe fields.

In an exemplary embodiment a magnetic brush roll 42 approximately 15inches long was employed having magnets 45 and 46 suspended therein ofapproximately 14 /2 inches long. The magnets 22 and 23, in accordancewith this invention to provide the stationary magnetic brush baffles 20,were selected to be approximately 1% inches long. This specific example,however, is not meant to be limitative of the invention.

Referring to FIG. 5, a magnetic field arrangement in accordance with thepreferred embodiment of this invention is shown. As shown in FIG. 5, thebafile forming magnet 22 has a magnetic field 61 associated therewithwhich is capable of forming a stationary magnetic brush 21. Thestationary magnetic brush 21 does not extend, however, over the entiregap 57 between the roll surface 44 and the bottom of the housing 41 inorder to allow developer material flow in the gap 60 between the brush21 and the roll surface 44. In operation, the field 61 cooperates withthe field 62 of the magnet 46 so that a magnetic brush will be formedover the entire gap 57 between the housing 41 and the roll surface 44which is made up of two components. The first component will comprisethe stationary brush 21 of this invention. The second component liesbetween the end of the stationary brush 21 and the roll surface 44 andcomprises the moving magnetic brush 47 formed by the field associatedwith the pick-up magnet 46.

In accordance with an exemplary embodiment the field intensity of thestationary brush forming magnet 22 0.1 inches above the magnet wasselected to be from about 260 to about 300 gauss. This shouldapproximate the field intensity at the interior surface of the housing41 adjacent the magnet 22. The field intensity of the pick-up magnet 46measured about 0.060 inches below the applicator roll surface wasapproximately 150 gauss. The gap 57 was about 0.1 inches. In anapparatus employing these magnets a stationary magnetic brush was formedwhich did not extend over the entire gap 57 between the roll 42 and theinterior of the housing 41.

Referring now to FIG. 6, an alternative embodiment in accordance withthe present invention is shown. In this embodiment the field strength ofthe stationary brush forming magnet 22 has been substantially in creasedto overcome the field of the pick-up magnet 46 so as to form astationary brush over the entire gap 57 between the interior of thehousing 41 and the roll surface 44. This type of baffle is not preferredin accordance with this invention, but is included in the broad scope ofthe invention. Referring again to FIG. 3, it is apparent that if astationary baffle brush 21' is formed over the entire gap 57 between theinterior of the housing 41 and the roll surface 44, the degree to whichthe stationary brushes project axially inwardly of the roll surfacewould have to be reduced. To provide axially shorter brushes 21' themagnets 22 and 23 would have to be reduced in length as shown in phantomby lines 25 and 26. In accordance with this embodiment the distancebetween the stationary brushes 21' in the axial direction of the rollwould have to be sufficiently large to permit a development brush 47 tobe formed having an operative length sufficient to cover the entire copysheet 36.

While this embodiment would be operative to reduce developer flow at theends 54 and 55 of the roll 42, it would not do so to the same degree asthe embodiment of FIG. 5. This is because the fringe fields 7 and 8extend into the operative length of the development brush 47. Therefore,by blocking off only that portion of the brush 47 which is not operativeto develop the image, the ends of the brush will still include anincreased developer flow due to the effect of the fringe fields, and,therefore, a somewhat increased background development as compared tothe development by the axial center of the brush.

Referring now to FIGS. 70 and 7b, there is shown the effect of astationary brush forming magnet 22 having a substantially uniformcross-section over its entire length. The stationary brush 21 formed bythis magnet has a substantially uniform height over substantially theentire length of the magnet and the height then falls off very rapidlyat the end of the magnet. This should result approximately, as shown inFIG. 7a, in a fairly abrupt change in developer flow rate along thelength of the roll 42 and, therefore, in a corresponding abrupt changein the density of the developer in the brush 47 during development ofthe image and a noticeable corresponding abrupt change in the density ofthe image transferred to the copy sheet 36.

Referring to FIGS. 8a and 8b, there is shown a stationary brush formingmagnet 22 which has a wedge shaped form wherein the thickness of themagnet decreases as the magnet projects inwardly of the applicator roll42. The stationary brush 21 formed by this type of magnet 22 isillustrated in FIG. 8b. As shown therein, there is a gradual reductionin the height of the stationary brush 21 the further it extends inwardlyof the development roll 42.

Referring to FIG. 8a, the flow rate of the developer is shown extendingin from the housing 41. The flow rate shown changes gradually insubstantial correspondence to the height of the stationary brush. Thisgradual change in flow rate allows the density of the developer in thedevelopment brush 47 to also change gradually so that the density changein the image on the copy sheet also changes more gradually, therefore,creating an acceptable appearance. Therefore, it is quite apparent froma consideration of FIGS. 7 and 8 that the use of a wedge shapedstationary brush forming magnet 22 and 23 is highly desirable andpreferred in accordance with this invention.

It is also apparent that it is preferred in accordance with thisinvention to position the stationary brush forming magnets 22 and 23externally of the housing 41. Positioning the magnets externally of thehousing allows greater flexibility since one or both magnets could bechanged in the event that developer flow at the ends of the roll 42 isnot acceptable. If desired, however, the magnets can be positionedinternally of the housing 41 or the magnetic brush rolls 42 and 43. Thisapproach could well be used, for example, with stationary brushes 21which extend over the entire gap 57 between the roll surface 44 and thehousing 41.

While the stationary brushes flow baffles 21 have been described withreference to their use in conjunction with the applicator roll 42, theycould be employed with other magnetic brush rolls, if desired.

It has been found desirable to provide impervious flow blocking membersas shown in FIG. 2. The members have a cross-section as shown and extendinwardly of the roll 42 an amount similar to the brushes 21 of theembodiment of FIG. 6. They are located between the supply means 52 andthe baffles 20. The members 70 further improve the regulation ofdeveloper flow rate at the ends of the roll 42.

The patents and texts referred to specifically in this application areintended to be incorporated by reference into the application.

It is apparent that there has been provided in accordance with thisinvention, a support member, process and apparatus which fully satisfiesthe objects, means and advantages set forth hereinbefore. While thcinvention has been described in conjunction with specific embodimentsthereof, it is evident that many alterna' tives, modifications andvariations will be apparent to those skilled in the art in light of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications and variations as fall within the spirit andbroad scope of the appended claims.

What is claimed is:

1. In a development apparatus for developing electrostatic images uponan image bearing surface by the application of developer theretocomprising: a moving member for supporting a first magnetic brush ofsaid developer; first magnetic field generating means for forming saidfirst magnetic brush so that it extends out from said moving member witha first height; the improvement wherein, said apparatus furtherincludes:

means for reducing the height of said first magnetic brush, said heightreducing means comprising a stationary member for supporting a secondmagnetic brush of said developer, said stationary member being spacedfrom'said moving member and second magnetic field generating means forforming said second magnetic brush so that it extends out from saidstationary member toward said moving member so as to engage said firstmagnetic brush to reduce said first height.

2. An apparatus as in claim 1, further including a developer supplymeans, and wherein said moving member comprises a development means forapplying developer to said imaging bearing surface, said developmentmeans extending across said image bearing surface and having first andsecond opposing ends and first and second end portions extendinginwardly from said ends, and further including means for moving saidmoving member between said supply means and a development zone.

3. An apparatus as in claim 2, wherein said first and said secondmagnetic field generating means comprise permanent magnets.

4. An apparatus as in claim 3, further including a housing substantiallyenclosing said development apparatus and having an opening at saiddevelopment zone to provide communication between said development meansand said moving image bearing surface and wherein said second magneticfield generating means is positioned externally of said housing.

5. An apparatus as in claim 4, wherein said stationary member comprisesa portion of said housing.

6. An apparatus as in claim 2, wherein said second magnetic fieldgenerating means are positioned between said supply means and saiddevelopment zone and extend inwardly of each of the ends of saiddevelopment means a given amount and have a limited extension in thedirection of movement of said development means, whereby said secondmagnetic brushes as formed tend to limit the flow of developer at theendportions of said development means.

7. An apparatus as in claim 5, further including a 7 housingsubstantially enclosing said development appa- 8. An apparatus as inclaim 6 wherein said second magnetic field generating means comprisepermanent magnets positioned at the ends of said housing.

9. An apparatus as in claim 7, wherein said permanent magnets have awedge shaped portion wherein the thickness of said magnets decreases thefurther said magnets extend inwardly of said development means.

10. An apparatus as in claim 8, further including fiow blocking membersextending inwardly of each of the ends of said development means saidmembers being positioned between said supply means and said secondmagnetic field generating means.

11. A development apparatus for developing electrostatic images upon animage bearing surface by the application of developer theretocomprising:

a moving member for supporting a first magnetic brush of said developer,said member having first and second opposing ends and first and secondend portions extending inwardly from said ends;

a stationary member for supporting a second magnetic brush of saiddeveloper, said stationary member being spaced from said moving memberso as to define a gap extending from said moving member to saidstationary member;

first magnetic field generating means for forming said first magneticbrush so that it extends out from said moving member toward saidstationary member in said gap;

second magnetic field generating means for forming said second magneticbrush so that it extends out from said stationary member toward saidmoving member over the entire of said gap,

said second magnetic field generating means extending inwardly of theends of said moving member a given amount and having a limited extensionin the direction of movement of said member;

whereby said second magnetic brushes as formed tend to limit the flow ofdeveloper at the end portions of said member.

12. An apparatus as in claim 11, further including a developer supplymeans, and wherein said moving member comprises a development means forapplying developer to said imaging bearing surface, said developmentmeans extending across said image bearing surface, and further includingmeans for moving said moving member between said supply means and adevelopment zone.

13. An apparatus as in claim 12, further including a housingsubstantially enclosing'said development apparatus and having an openingat said development zone to provide communication between saiddevelopment means and said moving image bearing surface and wherein saidsecond magnetic field generating means are positionedextemally of saidhousing.

14. An apparatus as in claim 13, wherein said second second magneticfield generating means.

' UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In Claim 7, line place the number In Claim 8, line place the number InClaim 9, line place the number l, delete the number "6", and insert inits 1, delete the number "7", and insert in its t In Claim 10, line 1,delete the number "8" and insert in its place the number [SEAL]Twentieth Day of July 1976 A ttes t:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner oj'Patentsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 2 3,915,121 DATED October 28, 1975 INVENTOR( IDavid G. Wilcox It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

In Claim 7, line I, delete the number "5", and insert in its place thenumber -6--.

In Claim 8, line 1, delete the number "6" and insert in its place thenumber --7.

In Claim 9, line 1, delete the number "7" and insert in its place thenumber -8-.

In Claim 10, line 1, delete the number "8" and insert in its place thenumber --9.

Signed and Scaled this Twentieth Day of July 1976 [SEAL] A ttes t.

RUTH C. MASON C. MARSHALL DANN A nesting Officer Commissioner ufPatenrsand Trademarks

1. In a development apparatus for developing electrostatic images uponan image bearing surface by the application of developer theretocomprising: a moving member for supporting a first magnetic brush ofsaid developer; first magnetic field generating means for forming saidfirst magnetic brush so that it extends out from said moving member witha first height; the improvement wherein, said apparatus furtherincludes: means for reducing the height of said first magnetic brush,said height reducing means comprising a stationary member for supportinga second magnetic brush of said developer, said stationary member beingspaced from said moving member and second magnetic field generatingmeans for forming said second magnetic brush so that it extends out fromsaid stationary member toward said moving member so as to engage saidfirst magnetic brush to reduce said first height.
 2. An apparatus as inclaim 1, further including a developer supply means, and wherein saidmoving member comprises a development means for applying developer tosaid imaging bearing surface, said development means extending acrosssaid image bearing surface and having first and second opposing ends andfirst and second end portions extending inwardly from said ends, andfurther including means for moving said moving member between saidsupply means and a development zone.
 3. An apparatus as in claim 2,wherein said first and said second magnetic field generating meanscomprise permanent magnets.
 4. An apparatus as in claim 3, furtherincluding a housing substantially enclosing said development apparatusand having an opening at said development zone to provide communicationbetween said development means and said moving image bearing surface andwherein said second magnetic field generating means is positionedexternally of said housing.
 5. An apparatus as in claim 4, wherein saidstationary member comprises a portion of said housing.
 6. An apparatusas in claim 2, wherein said second magnetic field generating means arepositioned between said supply means and said development zone andextend inwardly of each of the ends of said development means a givenamount and have a limited extension in the direction of movement of saiddevelopment means, whereby said second magnetic brushes as formed tendto limit the flow of developer at the end portions of said developmentmeans.
 7. An apparatus as in claim 5, further including a housingsubstantially enclosing said development apparatus and having an openingat said development zone to provide communication between saiddevelopment means and said moving image bearing surface and wherein saidsecond magnetic field generating means are positioned externally of saidhousing.
 8. An apparatus as in claim 6 wherein said second magneticfield generating means comprise permanent magnets positioned at the endsof said housing.
 9. AN apparatus as in claim 7, wherein said permanentmagnets have a wedge shaped portion wherein the thickness of saidmagnets decreases the further said magnets extend inwardly of saiddevelopment means.
 10. An apparatus as in claim 8, further includingflow blocking members extending inwardly of each of the ends of saiddevelopment means said members being positioned between said supplymeans and said second magnetic field generating means.
 11. A developmentapparatus for developing electrostatic images upon an image bearingsurface by the application of developer thereto comprising: a movingmember for supporting a first magnetic brush of said developer, saidmember having first and second opposing ends and first and second endportions extending inwardly from said ends; a stationary member forsupporting a second magnetic brush of said developer, said stationarymember being spaced from said moving member so as to define a gapextending from said moving member to said stationary member; firstmagnetic field generating means for forming said first magnetic brush sothat it extends out from said moving member toward said stationarymember in said gap; second magnetic field generating means for formingsaid second magnetic brush so that it extends out from said stationarymember toward said moving member over the entire of said gap, saidsecond magnetic field generating means extending inwardly of the ends ofsaid moving member a given amount and having a limited extension in thedirection of movement of said member; whereby said second magneticbrushes as formed tend to limit the flow of developer at the endportions of said member.
 12. An apparatus as in claim 11, furtherincluding a developer supply means, and wherein said moving membercomprises a development means for applying developer to said imagingbearing surface, said development means extending across said imagebearing surface, and further including means for moving said movingmember between said supply means and a development zone.
 13. Anapparatus as in claim 12, further including a housing substantiallyenclosing said development apparatus and having an opening at saiddevelopment zone to provide communication between said development meansand said moving image bearing surface and wherein said second magneticfield generating means are positioned externally of said housing.
 14. Anapparatus as in claim 13, wherein said second magnetic field generatingmeans comprise permanent magnets positioned at the ends of said housing.15. An apparatus as in claim 14, wherein said permanent magnets have awedge shaped portion wherein the thickness of said magnets decreases thefurther said magnets extend inwardly of said development means.
 16. Anapparatus as in claim 15, further including flow blocking membersextending inwardly of each of the ends of said development means saidmembers being positioned between said supply means and said secondmagnetic field generating means.